Voltmeter



L. DAPT.

VOLTMETER.

(No Model.)

No. 404,470. Patented June 4, 1889:

mith name y,

ogwgagzm y UNITED STATES PATENT OFFICE.

LEO DAFT, OF PLAINFIELD, NEW JERSEY.

VOLTMETER.

SPECIFICATION forming part of Letters Patent No. 404,470, dated June 4, 1889.

Application filed July 10, 1838.

To all whom it may concern.-

Be it known that I, LEO DAFT, a subject of the Queen of Great Britain, residing at Plainfield, Union county, State of New Jersey, United States of America, have invented certain new and useful Improvements in Volt 7 meters, of which the following is a full, clear, and exact specification.

My invention relates to voltmeters and ammeters which are specially adapted for central-station purposes, and it has for its object to produce a simple, cheap, and effective instrument which is not liable to get out of order or subject to delicate and frequent adjustments; and my invention consists in the construction and arrangement substantially as hereinafter set forth.

In the accompanying drawings, Figure 1 is a front View, partially in section, of a voltmeter embodying my invention; and'Fig. 2 is a vertical transverse section of the same.

Upon a suitable base is mounted a core B, of soft iron or other suitable magnetic material, around which is arranged a coil A of fine wire, the terminals of which are connected to the binding-posts mounted on the base. I The core B is provided with an extension 0, which is bifurcated or slotted, so as to form two arms, between which is mounted a cam-shaped armature D, of soft iron or some other suitable material, in such a manner as to freely swing between the adjustable pivots E F. Connected to this armature is an arm or finger H, which extends up in front of a suitable scale 1, arranged on a back board or support J, preferably having a flange K and inclosing glass front L. The shape of the arm D is such that when no current is flowing the pointer H will normally stand at zero on the scale, and will be held in such position by gravity.

Secured to the end of the core is an extension G, which is bent up parallelwith the out side of the coil, and upon its end it supports an adjustable piece G, preferablyin the form of an angle, and this extension, when used, is made fork-shaped, so as to permit a wider range of adjustment toward the armature D,

Serial No. 279,501. (No model.)

and so that even, if desired, the armature can pass between the forks of the extension.

The whole device as thus constructed is preferably inclosed in a suitable case to protect the parts from the elements.

Such being the construction, the operation of the instrument is as follows: When an electric current passes through the coils A, surrounding the core, the core becomes magnetized, and the extension 0 thereof, which forms one pole of the core, will excite the armature by ind uetion with magnetism of the same po larity as the end of the core. The armature D is suspended in a uniform field of force,

by the repulsive force of the pole, and I have found that the strength of thisrepulsion is proportional to the difference of potential of the current passing through the coil, and the finger or pointer is thus made to indicate on the scale the voltage of the current passing through. It will be understood, of course, thatthe extension G becomes magnetic'by extension 0, and I have found that this extension can be so. adjustedwith relation to the armature as to act in conjunction with the repulsive force to regulate to a certain extent the eifect of the current on the armature; but this extension G may be dispensed with when it is not desired to measure the minor deflections, and in an ordinary station-instrument, where the usual limits of current are not less than twenty-five to one hundred volts, it is not necessary. It will be understood, of course, that this extension G acts first to attract the armature and to assist the repulsion; but after the armature has moved to a certain degree the extension G acts in opposition to the extension 0 and assists to retard and restrict the increasing repulsion between the armature and the extension 0.

It will thus be seen that the armature, which is of such a shape that it almost exactly corresponds to the graphic delineation of the increasing energy of repulsion with the increased intensity of the magnetic field, is supported normally in a uniform field, and is and is repelled from the field of the extension.

induction and is of an opposite polarity to the directly acted upon by the varying repulsive force due to the changes in the current through the coil, and that very little adjustment to the device is necessary, and especially when the extension G is not used.

What I claim, and desire to secure by Letters Patent, is

1. A voltmeter consisting of a coil, the core of which is provided with a slotted extension supporting a cam-shaped armature Within the slot, and having a pointer connected to the armature, whereby the cam-shaped armature is normally maintained in a uniform field of force, and is operated by repulsion in accord- 

